public class ListNode {
      int val;
      ListNode next;
      ListNode() {

      }
      ListNode(int val) {
       this.val = val;
      }
      ListNode(int val, ListNode next) {
       this.val = val; this.next = next;
      }

    @Override
    public String toString() {
        String str = "" + val;
        while (next != null) {
            str = str + " " + next.val;
            next = next.next;
        }
        return str;
    }
}


